The goal of this research is to understand the molecular interactions between rRNA and mRNA that are pertinent in selection in the A site. Specific Aim 1: Is the 16S ribosomal RNA triple mutant G530A, A1408C/G/L, and A1492G functionally comparable to wild type ribosomes? Specific Aim 2: What is the effect of interactions between C1054 and the base following UGA on release factor 2 selection. A literature survey of human genetic defects found that there are 179 unique nonsense mutations that result in disease (Atkinson, 1994). The effect of these mutations varies across a wide range including ovarian cancer, cystic fibrosis, and sex reversal. Understanding the mechanisms of selection will aid the development of drug and genetic therapies.